Silicon-based materials containing gallium and methods of forming the same

ABSTRACT

A ceramic component is generally provided that includes a silicon-based layer comprising a silicon-containing material (e.g., a silicon metal and/or a silicide) and about 0.001% to about 85% of a Ga-containing compound. For example, the silicon-based layer can be a bond coating directly on the surface of the substrate. Alternatively or additionally, the silicon-based layer can be an outer layer defining a surface of the substrate, with an environmental barrier coating on the surface of the substrate. Gas turbine engines are also generally provided that include such a ceramic component.

FIELD OF THE INFORMATION

The present invention generally relates to including gallium (Ga)compounds within a silicone based coating. In particular, silicon-basedcoatings (e.g., silicon bond coatings) that include Ga are generallyprovided for use in environmental barrier coatings for ceramiccomponents.

BACKGROUND OF THE INVENTION

Higher operating temperatures for gas turbine engines are continuouslybeing sought in order to improve their efficiency. However, as operatingtemperatures increase, the high temperature durability of the componentsof the engine must correspondingly increase. Significant advances inhigh temperature capabilities have been achieved through the formulationof iron, nickel, and cobalt-based superalloys. Still, with many hot gaspath components constructed from super alloys, thermal barrier coatings(TBCs) can be utilized to insulate the components and can sustain anappreciable temperature difference between the load-bearing alloys andthe coating surface, thus limiting the thermal exposure of thestructural component.

While superalloys have found wide use for components used throughout gasturbine engines, and especially in the higher temperature sections,alternative lighter-weight substrate materials have been proposed, suchas ceramic matrix composite (CMC) materials. CMC and monolithic ceramiccomponents can be coated with environmental barrier coatings (EBCs) toprotect them from the harsh environment of high temperature enginesections. EBCs can provide a dense, hermetic seal against the corrosivegases in the hot combustion environment.

Silicon carbide and silicon nitride ceramics undergo oxidation in dry,high temperature environments. This oxidation produces a passive,silicon oxide scale on the surface of the material. In moist, hightemperature environments containing water vapor, such as a turbineengine, both oxidation and recession occurs due to the formation of apassive silicon oxide scale and subsequent conversion of the siliconoxide to gaseous silicon hydroxide. To prevent recession in moist, hightemperature environments, environmental barrier coatings (EBC's) aredeposited onto silicon carbide and silicon nitride materials.

Currently, EBC materials are made out of rare earth silicate compounds.These materials seal out water vapor, preventing it from reaching thesilicon oxide scale on the silicon carbide or silicon nitride surface,thereby preventing recession. Such materials cannot prevent oxygenpenetration, however, which results in oxidation of the underlyingsubstrate. Oxidation of the substrate yields a passive silicon oxidescale, along with the release of carbonaceous or nitrous oxide gas. Thecarbonaceous (i.e., CO, CO₂) or nitrous (i.e., NO, NO₂, etc.) oxidegases cannot escape out through the dense EBC and thus, blisters form.The use of a silicon bond coat has been the solution to this blisteringproblem to date. The silicon bond coat provides a layer that oxidizes(forming a passive silicon oxide layer beneath the EBC) withoutliberating a gaseous by-product.

However, the presence of a silicon bond coat limits the uppertemperature of operation for the EBC because the melting point ofsilicon metal is relatively low. In use, a thermally grown oxide (TGO)layer of silicon oxide forms on the top surface of the silicon metalbond coat of a multilayer EBC system. This silicon oxide scale remainsamorphous at temperatures of 1200° C. or lower, sometimes even attemperatures of 1315° C. or lower, although this property is alsodependent on the time the bond coat is exposed to this temperature. Athigher temperatures, or when minor amounts of steam penetrate throughthe EBC to the bond coat, the silicon oxide scale crystallizes (e.g.,into cristoblate), which undergoes phase transition accompanied by largevolume change on cooling. The volume change leads to EBC coating spall.

As such, it is desirable to improve the properties of a silicon bondcoat in the EBC to achieve a higher operational temperature limit forthe EBC.

BRIEF DESCRIPTION OF THE INVENTION

Aspects and advantages of the invention will be set forth in part in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

A ceramic component is generally provided that includes a silicon-basedlayer comprising a silicon-containing material (e.g., a silicon metaland/or a silicide) and about 0.001% to about 85% of a Ga-containingcompound. For example, the silicon-based layer can be a bond coatingdirectly on the surface of the substrate. Alternatively or additionally,the silicon-based layer can be an outer layer defining a surface of thesubstrate, with an environmental barrier coating on the surface of thesubstrate. Gas turbine engines are also generally provided that includesuch a ceramic component.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims. The accompanying drawings, which areincorporated in and constitute a part of this specification, illustrateembodiments of the invention and, together with the description, serveto explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth in the specification, which makes reference to the appended Figs.,in which:

FIG. 1 is a cross-sectional side view of an exemplary ceramic componentincluding a silicon-based layer;

FIG. 2 is a cross-sectional side view of the exemplary ceramic componentof FIG. 1 including a thermally grown oxide layer on the silicon-basedlayer;

FIG. 3 is a cross-sectional side view of another exemplary ceramiccomponent including a silicon-based layer;

FIG. 4 is a cross-sectional side view of the exemplary ceramic componentof FIG. 3 including a thermally grown oxide layer on the silicon-basedlayer; and

FIG. 5 is a schematic cross-sectional view of an exemplary gas turbineengine according to various embodiments of the present subject matter.

Repeat use of reference characters in the present specification anddrawings is intended to represent the same or analogous features orelements of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference now will be made in detail to embodiments of the invention,one or more examples of which are illustrated in the drawings. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations can be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment can be used with another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncovers such modifications and variations as come within the scope of theappended claims and their equivalents.

As used herein, the terms “first”, “second”, and “third” may be usedinterchangeably to distinguish one component from another and are notintended to signify location or importance of the individual components.

Chemical elements are discussed in the present disclosure using theircommon chemical abbreviation, such as commonly found on a periodic tableof elements. For example, hydrogen is represented by its common chemicalabbreviation H; helium is represented by its common chemicalabbreviation He; and so forth. As used herein, “Ln” refers to a rareearth element or a mixture of rare earth elements. More specifically,the “Ln” refers to the rare earth elements of scandium (Sc), yttrium(Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd),promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium(Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm),ytterbium (Yb), lutetium (Lu), or mixtures thereof.

In the present disclosure, when a layer is being described as “on” or“over” another layer or substrate, it is to be understood that thelayers can either be directly contacting each other or have anotherlayer or feature between the layers, unless expressly stated to thecontrary. Thus, these terms are simply describing the relative positionof the layers to each other and do not necessarily mean “on top of”since the relative position above or below depends upon the orientationof the device to the viewer.

Silicon-based coatings that include Ga are generally provided for usewith environmental barrier coatings for ceramic components, along withtheir methods of formation. In particular embodiments, silicon-basedbond coatings for environmental barrier coatings (EBCs) are generallyprovided for high temperature ceramic components, along with methods ofits formation and use. In particular, the silicon-based bond coatingincludes a component containing Ga for preventing crystallization of athermal growth oxide (“TGO”) on silicon-based bond coating in an EBC,which in turn prevents spall of the coating caused by suchcrystallization of the TGO. That is, the introduction of Ga within thesilicon-based bond coating keeps the TGO (i.e., the SiO) in an amorphousphase. Accordingly, the operating temperature of the silicon-based bondcoating (and thus the TGO and EBC coating) can be increased.Additionally, the inclusion of Ga can inhibit and preventcrystallization of the TGO without greatly accelerating the growth rateof the TGO. Additionally, Ga-containing components have limited reactionwith and/or solubility into in silicon oxide, which can limit the rateof oxide scale growth.

FIGS. 1-4 show exemplary embodiments of a ceramic component 100 formedfrom a substrate 102 and a silicon-based layer 104 a (FIG. 1), 104 b(FIG. 3), respectively. Each of the silicon-based layers 104 a, 104 bincludes a silicon-containing material and about 0.001% to about 85% ofa Ga-containing compound, such as about 1% to about 60% by weight of aGa-containing compound (e.g., about 1% to about 50% by weight, such asabout 1% to about 25% by weight). Generally, the Ga-containing compoundis unreactive with the composition of the silicon-based layer 104 a(e.g., silicon metal).

In one embodiment, the silicon-based layer 104 a may include theGa-containing compound and a silicon-containing material (e.g., siliconmetal, a silicide, etc.) in continuous phases that are intertwined witheach other. For example, the silicon-containing material and theGa-containing compound are intertwined continuous phases having about0.001% to about 85% by volume of the Ga-containing compound, such asabout 1% to about 60% by volume (e.g., about 40% to about 60% by volumeof the Ga-containing compound). For example, the silicon-based layer 104a can include the Ga-containing compound in about 15% by volume to about85% by volume, with the balance being the silicon containing compound.

In another embodiment, the Ga-containing compound forms a plurality ofdiscrete phases dispersed within the silicon-containing material (e.g.,within a continuous phase of the silicon-containing material), such asdiscrete particulate phases. In such an embodiment, the silicon-basedlayer 104 a can include about 0.001% to about 40% by volume of theGa-containing compound, such as about 1% to about 25% by volume (e.g.,about 1% to about 10% by volume of the Ga-containing compound).

In one particular embodiment, the substrate 102 is formed from a CMCmaterial (e.g., a silicon based, non-oxide ceramic matrix composite). Asused herein, “CMCs” refers to silicon-containing, or oxide-oxide, matrixand reinforcing materials. As used herein, “monolithic ceramics” refersto materials without fiber reinforcement (e.g., having the matrixmaterial only). Herein, CMCs and monolithic ceramics are collectivelyreferred to as “ceramics.”

Some examples of CMCs acceptable for use herein can include, but are notlimited to, materials having a matrix and reinforcing fibers comprisingnon-oxide silicon-based materials such as silicon carbide, siliconnitride, silicon oxycarbides, silicon oxynitrides, and mixtures thereof.Examples include, but are not limited to, CMCs with silicon carbidematrix and silicon carbide fiber; silicon nitride matrix and siliconcarbide fiber; and silicon carbide/silicon nitride matrix mixture andsilicon carbide fiber. Furthermore, CMCs can have a matrix andreinforcing fibers comprised of oxide ceramics. Specifically, theoxide-oxide CMCs may be comprised of a matrix and reinforcing fiberscomprising oxide-based materials such as aluminum oxide (Al₂O₃), silicondioxide (SiO₂), aluminosilicates, and mixtures thereof. Aluminosilicatescan include crystalline materials such as mullite (3Al₂O₃ 2SiO₂), aswell as glassy aluminosilicates.

In the embodiment of FIG. 1, the substrate 102 defines a surface 103having a coating 106 formed thereon. The coating 106 includes thesilicon-based layer 104 a and an environmental barrier coating 108. Inone particular embodiment, the silicon-based layer 104 a is a bondcoating, where the silicon containing material is silicon metal, asilicide (e.g., a rare earth silicide, a molybdenum silicide, a rheniumsilicide, or mixtures thereof), or a mixture thereof. In one embodiment,a composition is generally provided that includes silicon metal and theGa-containing compound, such as in the relative amounts described above(e.g., about 0.01 to about 85% by volume). In an alternative embodiment,a composition is generally provided that includes a silicide (e.g., arare earth silicide, a molybdenum silicide, a rhenium silicide, ormixtures thereof) and the Ga-containing compound, such as in therelative amounts described above (e.g., about 0.01 to about 85% byvolume).

During use, a thermally grown oxide (“TGO”) layer forms on the surfaceof the bond coating. For example, a layer of silicon oxide (sometimesreferred to as “silicon oxide scale” or “silica scale”) forms on a bondcoating of silicon metal and/or a silicide. Referring to FIG. 2, athermally grown oxide layer 105 (e.g., silicon oxide) is shown directlyon the silicon-based layer 104 a (e.g., a bond coating with the siliconcontaining material being silicon metal and/or a silicide), as formsduring exposure to oxygen (e.g., during manufacturing and/or use) of thecomponent 100. Due to the presence of the Ga-containing compound withinthe silicon-based layer 104 a, the thermally grown oxide layer 105remains substantially amorphous at its operating temperature, with the“operating temperature” referring to the temperature of the thermallygrown oxide layer 105. For example, for silicon metal bond coatings, theTGO layer may remain amorphous at operating temperatures of about 1415°C. or less (e.g., about 1200° C. to about 1410° C.), which is just belowthe melting point of the silicon-based bond coating (Si metal has amelting point of about 1414° C.). In another example, for silicide bondcoatings, the TGO layer may remain amorphous at operating temperaturesof about 1485° C. or less (e.g., about 1200° C. to about 1415° C.),which is just below the maximum use temperature of the CMC. Withoutwishing to be bound by any particular theory, it is believed thatgallium in the silicon-based layer 104 a migrates into the thermallygrown oxide layer 105 and inhibits crystallization of the thermallygrown oxide layer (e.g., silicon oxide) that would otherwise occur atthese temperatures. Without wishing to be bound by any particulartheory, it is presently believed that Ga inhibits impurities such as Naand/or K from causing crystallization of the amorphoussilicon-containing material.

In the embodiment shown in FIGS. 1 and 2, the silicon-based layer 104 ais directly on the surface 103 without any layer therebetween. However,in other embodiments, one or more layers can be positioned between thesilicon-based layer 104 a and the surface 103.

FIG. 3 shows another embodiment of a ceramic component 100 with thesubstrate 102 having an outer layer 104 b that defines a surface 103 ofthe substrate 102. That is, the outer layer 104 b is integral with thesubstrate 102. In this embodiment, the outer layer 104 b is thesilicon-based layer, and a coating 106 is on the surface 105. Thecoating 106 may include an environmental barrier coating 108 and/orother layers (e.g., a bond coating, etc.). In one embodiment, the outerlayer 104 b can be a silicon-containing monolithic ceramic layer. Forexample, the outer layer 104 b may include silicon carbide. In oneembodiment, the substrate 102 may include the outer layer 104 b (e.g.,including silicon carbide as a monolithic ceramic layer) on a pluralityof CMC plies forming the remaining portion of the substrate.

FIG. 4 shows a thermally grown oxide layer 105 (e.g., silicon oxide)directly on the silicon-based layer 104 b (e.g., a bond coating with thesilicon containing material being silicon metal), as forms duringexposure to oxygen (e.g., during manufacturing and/or use) of thecomponent 100. Due to the presence of the Ga-containing compound withinthe silicon-based layer 104 b, the thermally grown oxide layer 105remains substantially amorphous at the operating temperature of thethermally grown oxide layer 105. Without wishing to be bound by anyparticular theory, it is believed that gallium in the silicon-basedlayer 104 b migrates into the thermally grown oxide layer 105 andinhibits crystallization of the thermally grown oxide layer (e.g.,silicon oxide) that would otherwise occur at these temperatures.

As stated, a Ga-containing compound is included within the silicon-basedlayer 104 a, 104 b, no matter the particular positioning of thesilicon-based layer 104 in the ceramic component 100. In particularembodiments, the Ga-containing compound is in the form of an oxide or anitride. For example, the Ga-containing compound can be gallium nitride(GaN), gallium oxide (Ga₂O₃), or a mixture thereof. In the embodimentwhere the Ga-containing compound includes gallium oxide, the galliumoxide can be doped within another oxide. For example, the Ga-containingcompound can be zirconium oxide (ZrO₂), hafnium oxide (HfO₂), or acombination thereof doped with up to about 10 mole % of Ga₂O₃.

In one embodiment, the Ga-containing compound can be agallium-metal-oxide. For example, the Ga-containing compound can have,in one embodiment, a formula of:

Ga_(2-x)M_(x)O₃

where M is In with x being 0 to less than 2, Al with x being 0 to about1.4, B with x being 0 to about 1.4, Fe with x being 0 to about 1.4, or amixture thereof. In one embodiment, M is In with x being greater than 0to less than 2, Al with x being greater than 0 to about 1.4, B with xbeing greater than 0 to about 1.4, Fe with x being greater than 0 toabout 1.4, or a mixture thereof, such that at least one other metal (In,Al, B, and/or Fe) is present in the gallium-metal-oxide.

In one embodiment, the Ga-containing compound can be a rareearth-gallium-oxide. For example, the Ga-containing compound can have,in one embodiment, a formula of:

Ln_(4-x)D_(x)Ga_(2-y)In_(y)O₉

where Ln is La, Ce, Pr, Nd, Pm, Sm, or a mixture thereof; D is La, Ce,Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or a mixturethereof, with D being different than Ln (i.e., D is a different elementor combination of elements than Ln); and y is 0 to about 1 (e.g., 0≦y≦1,such as 0≦y≦0.5). In one particular embodiment, y is greater than 0 toabout 1 (e.g., 0<y≦1, such as 0<y≦0.5). If D is La, Ce, Pr, Nd, Pm, Sm,or a mixture thereof (i.e., having an atomic radius of Sm or larger),then x is 0 to less than 4 (e.g., 0<x<4, such as 0<x≦about 2). However,if D is Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or a mixture thereof (i.e.,having an atomic radius that is smaller than Sm), then x is 0 to about 2(e.g., 0<x<2, such as 0<x≦about 1).

In another embodiment, the Ga-containing compound can have a formula of:

Ln₃Ga_(5-x)M_(x)O₁₂

where Ln is Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm,Yb, Lu, or a mixture thereof; and M is In with x being 0 to less than 5(e.g., 0≦x<5, such as 0<x≦2.5), Al with x being 0 to less than 5 (e.g.,0≦x<5, such as 0<x≦2.5), Fe with x being 0 to less than 5 (e.g., 0≦x<5,such as 0<x≦2.5), B with x being 0 to about 2.5 (e.g., 0≦x≦2.5), or acombination thereof. In one particular embodiment, M is B, with x beinggreater than 0 to about 2.5 (e.g., 0<x≦2.5), such as about 0.1 to about2 (e.g., 0.1≦x≦2). In one embodiment, x is greater than 0 (e.g., 0.1 toabout 2) such that at least one of M (e.g., In, Al, Fe, and/or B) ispresent in the Ga-containing compound.

In one embodiment, the Ga-containing compound can have a formula of:

Ln_(2-x-y) Ga_(x)In_(y)Si₂O₇

where Ln is Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm,Yb, Lu, or a mixture thereof; x is greater than 0 to about 1; and y is 0to about 1. In one embodiment, the sum of x and y is greater than 0 upto about 1 (i.e., 0<(x+y)≦about 1), such as about greater than 0 up toabout 0.5 (i.e., 0<(x+y)≦about 0.5). In one embodiment, y is 0.

In one embodiment, the Ga-containing compound can have a formula of:

Ln_(2-x-y) Ga_(x)In_(y)Si₂O₅

where Ln is Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm,Yb, Lu, or a mixture thereof; x is greater than 0 to about 1; and y is 0to about 1. In one embodiment, the sum of x and y is greater than 0 upto about 1 (i.e., 0<(x+y)≦about 1), such as about greater than 0 up toabout 0.5 (i.e., 0<(x+y)≦about 0.5). In one embodiment, y is 0.

The environmental barrier coating 108 of FIGS. 1-4 can include anycombination of one or more layers formed from materials selected fromtypical EBC or TBC layer chemistries, including but not limited to rareearth silicates (mono- and di-silicates), mullite, barium strontiumaluminosilicate (BSAS), hafnia, zirconia, stabilized hafnia, stabilizedzirconia, rare earth hafnates, rare earth zirconates, rare earthgallates, etc.

The ceramic component 100 of FIGS. 1-4 is particularly suitable for useas a component found in high temperature environments, such as thosepresent in gas turbine engines, for example, combustor components,turbine blades, shrouds, nozzles, heat shields, and vanes. Inparticular, the turbine component can be a CMC component positionedwithin a hot gas flow path of the gas turbine such that the coatingforms an environmental barrier coating on the component to protect thecomponent within the gas turbine when exposed to the hot gas flow path.

FIG. 5 is a schematic cross-sectional view of a gas turbine engine inaccordance with an exemplary embodiment of the present disclosure. Moreparticularly, for the embodiment of FIG. 5, the gas turbine engine is ahigh-bypass turbofan jet engine 10, referred to herein as “turbofanengine 10.” As shown in FIG. 5, the turbofan engine 10 defines an axialdirection A (extending parallel to a longitudinal centerline 12 providedfor reference) and a radial direction R. In general, the turbofan 10includes a fan section 14 and a core turbine engine 16 disposeddownstream from the fan section 14. Although described below withreference to a turbofan engine 10, the present disclosure is applicableto turbomachinery in general, including turbojet, turboprop andturboshaft gas turbine engines, including industrial and marine gasturbine engines and auxiliary power units.

The exemplary core turbine engine 16 depicted generally includes asubstantially tubular outer casing 18 that defines an annular inlet 20.The outer casing 18 encases, in serial flow relationship, a compressorsection including a booster or low pressure (LP) compressor 22 and ahigh pressure (HP) compressor 24; a combustion section 26; a turbinesection including a high pressure (HP) turbine 28 and a low pressure(LP) turbine 30; and a jet exhaust nozzle section 32. A high pressure(HP) shaft or spool 34 drivingly connects the HP turbine 28 to the HPcompressor 24. A low pressure (LP) shaft or spool 36 drivingly connectsthe LP turbine 30 to the LP compressor 22.

For the embodiment depicted, the fan section 14 includes a variablepitch fan 38 having a plurality of fan blades 40 coupled to a disk 42 ina spaced apart manner. As depicted, the fan blades 40 extend outwardlyfrom disk 42 generally along the radial direction R. Each fan blade 40is rotatable relative to the disk 42 about a pitch axis P by virtue ofthe fan blades 40 being operatively coupled to a suitable actuationmember 44 configured to collectively vary the pitch of the fan blades 40in unison. The fan blades 40, disk 42, and actuation member 44 aretogether rotatable about the longitudinal axis 12 by LP shaft 36 acrossan optional power gear box 46. The power gear box 46 includes aplurality of gears for stepping down the rotational speed of the LPshaft 36 to a more efficient rotational fan speed.

Referring still to the exemplary embodiment of FIG. 5, the disk 42 iscovered by rotatable front nacelle 48 aerodynamically contoured topromote an airflow through the plurality of fan blades 40. Additionally,the exemplary fan section 14 includes an annular fan casing or outernacelle 50 that circumferentially surrounds the fan 38 and/or at least aportion of the core turbine engine 16. It should be appreciated that thenacelle 50 may be configured to be supported relative to the coreturbine engine 16 by a plurality of circumferentially-spaced outletguide vanes 52. Moreover, a downstream section 54 of the nacelle 50 mayextend over an outer portion of the core turbine engine 16 so as todefine a bypass airflow passage 56 therebetween.

During operation of the turbofan engine 10, a volume of air 58 entersthe turbofan 10 through an associated inlet 60 of the nacelle 50 and/orfan section 14. As the volume of air 58 passes across the fan blades 40,a first portion of the air 58 as indicated by arrows 62 is directed orrouted into the bypass airflow passage 56 and a second portion of theair 58 as indicated by arrow 64 is directed or routed into the LPcompressor 22. The ratio between the first portion of air 62 and thesecond portion of air 64 is commonly known as a bypass ratio. Thepressure of the second portion of air 64 is then increased as it isrouted through the high pressure (HP) compressor 24 and into thecombustion section 26, where it is mixed with fuel and burned to providecombustion gases 66.

The combustion gases 66 are routed through the HP turbine 28 where aportion of thermal and/or kinetic energy from the combustion gases 66 isextracted via sequential stages of HP turbine stator vanes 68 that arecoupled to the outer casing 18 and HP turbine rotor blades 70 that arecoupled to the HP shaft or spool 34, thus causing the HP shaft or spool34 to rotate, thereby supporting operation of the HP compressor 24. Thecombustion gases 66 are then routed through the LP turbine 30 where asecond portion of thermal and kinetic energy is extracted from thecombustion gases 66 via sequential stages of LP turbine stator vanes 72that are coupled to the outer casing 18 and LP turbine rotor blades 74that are coupled to the LP shaft or spool 36, thus causing the LP shaftor spool 36 to rotate, thereby supporting operation of the LP compressor22 and/or rotation of the fan 38.

The combustion gases 66 are subsequently routed through the jet exhaustnozzle section 32 of the core turbine engine 16 to provide propulsivethrust. Simultaneously, the pressure of the first portion of air 62 issubstantially increased as the first portion of air 62 is routed throughthe bypass airflow passage 56 before it is exhausted from a fan nozzleexhaust section 76 of the turbofan 10, also providing propulsive thrust.The HP turbine 28, the LP turbine 30, and the jet exhaust nozzle section32 at least partially define a hot gas path 78 for routing thecombustion gases 66 through the core turbine engine 16.

Methods are also generally provided for coating a ceramic component. Inone embodiment, the method includes applying a bond coating directly ona surface of the ceramic component, where the bond coating comprises asilicon-containing material (e.g., silicon metal and/or a silicide) anda Ga-containing compound, such as described above.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they include structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

1. A ceramic component comprising: a substrate defining a surface; and asilicon-based layer forming a bond coating directly on the surface ofthe substrate, wherein the silicon layer comprises a silicon-containingmaterial and about 1% to 50% by weight of a Ga-containing compound,wherein the substrate is formed from a ceramic matrix composite (CMC)material.
 2. (canceled)
 3. The ceramic component as in claim 1, whereinthe silicon-containing material is silicon metal.
 4. The ceramiccomponent as in claim 3, wherein a thermally grown oxide is on the bondcoating, and wherein the thermally grown oxide layer remains amorphousup to an operating temperature of about 1415° C. or less.
 5. The ceramiccomponent as in claim 2, wherein the silicon-containing materialcomprises a silicide.
 6. The ceramic component as in claim 5, wherein athermally grown oxide is on the bond coating, and wherein the thermallygrown oxide layer remains amorphous up to an operating temperature ofabout 1485° C. or less.
 7. The ceramic component as in claim 5, whereinthe silicide comprises molybdenum silicide, rhenium silicide, or amixture thereof.
 8. The ceramic component as in claim 1, wherein thesilicon-based layer is an outer layer on the surface of the substrate;and the ceramic component further includes an environmental barriercoating on the silicone-based layer.
 9. The ceramic component as inclaim 8, wherein the substrate comprises the outer layer on a pluralityof CMC plies, and wherein the outer layer comprises silicon carbide. 10.The ceramic component as in claim 1, wherein the Ga-containing compoundcomprises Ga_(2-x)M_(x)O₃ where M is In with x being 0 to about 2, Alwith x being 0 to about 1.4, B with x being 0 to about 1.4, Fe with xbeing 0 to about 1.4, or a mixture thereof.
 11. The ceramic component asin claim 1, wherein the Ga-containing compound comprises ZrO₂, HfO₂, ora combination thereof doped with about 0.1% to about 10% by mole percentof Ga₂O₃.
 12. The ceramic component as in claim 1, wherein theGa-containing compound comprises a compound having a formula:Ln_(4-x)D_(x)Ga_(20y)In_(y)O₉ where: Ln is La, Ce, Pr, Nd, Pm, Sm, or amixture thereof; D is La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er,Tm, Yb, Lu, or a mixture thereof, where: D is not equal to Ln; if D isLa, Ce, Pr, Nd, Pm, Sm, or a mixture thereof, then x is 0 to less than4; if D is Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or a mixture thereof,then x is 0 to about 2; and y is 0 to about
 1. 13. The ceramic componentas in claim 12, wherein D is La, Ce, Pr, Nd, Pm, Sm, or a mixturethereof, and wherein x is greater than 0 to about
 2. 14. The ceramiccomponent as in claim 1, wherein the Ga-containing compound comprises acompound having a formula:Ln_(2-x-y)Ga_(x)In_(y)Si₂O₇ where Ln is Sc, Y, La, Ce, Pr, Nd, Pm, Sm,Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or a mixture thereof; x is greaterthan 0 to about 1; and y is 0 to about
 1. 15. The ceramic component asin claim 1, wherein the Ga-containing compound comprises a compoundhaving a formula:Ln_(2-x-y)Ga_(x)In_(y)Si₂O₅ where Ln is Sc, Y, La, Ce, Pr, Nd, Pm, Sm,Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or a mixture thereof; x is greaterthan 0 to about 1; and y is 0 to about
 1. 16. The ceramic component asin claim 1, wherein the Ga-containing compound comprises a compoundhaving a formula:Ln₃Ga_(5-x)M_(x)O₁₂ where Ln is Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd,Tb, Dy, Ho, Er, Tm, Yb, Lu, or a mixture thereof; and M is In with0≦x<5, Al with 0≦x<5, Fe with 0≦x<5, B with 0≦x≦2.5, or a combinationthereof.
 17. The ceramic component as in claim 16, where M is B; and xis about 0.1 to about
 2. 18. The ceramic component as in claim 1,wherein the Ga-containing compound comprises GaN.
 19. The ceramiccomponent as in claim 1, wherein the Ga-containing compound is selectedfrom the group consisting of: GaN; Ga₂O₃; Ga_(2-x)M_(x)O₃ where M is Inwith x being 0 to about 2, Al with x being 0 to about 1.4, B with xbeing 0 to about 1.4, Fe with x being 0 to about 1.4, or a mixturethereof; ZrO₂, HfO₂, or a combination thereof doped with up to about 10mole % of Ga₂O₃; Ln_(4-x)D_(x)Ga_(2-y)In_(y)O₉, where: Ln is La, Ce, Pr,Nd, Pm, Sm, or a mixture thereof; D is La, Ce, Pr, Nd, Pm, Sm, Eu, Gd,Tb, Dy, Ho, Er, Tm, Yb, Lu, or a mixture thereof, where D is not equalto Ln, if D is La, Ce, Pr, Nd, Pm, Sm, or a mixture thereof, then x is 0to less than 4, if D is Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or a mixturethereof, then x is 0 to about 2; and y is 0 to about 1;Ln₃Ga_(5-x)M_(x)O₁₂, where Ln is Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd,Tb, Dy, Ho, Er, Tm, Yb, Lu, or a mixture thereof; and M is In with0≦x<5, Al with 0≦x<5, Fe with 0≦x<5, B with 0≦x≦2.5, or a combinationthereof; and a mixture thereof.
 20. A gas turbine engine comprising theceramic component of claim
 1. 21. The ceramic component as in claim 3,wherein the silicon-based layer comprises the silicon metal in acontinuous phase.